Switchable valve trains of reciprocating internal combustion engines are known in various designs. In this regard, valve trains of individual cylinders or groups of cylinders of a reciprocating internal combustion engine can be deactivated by deactivating the transferrable valve lift and therefore, in conjunction with deactivating the fuel injection for the relevant cylinders, the fuel consumption and the CO2 and pollutant emissions of the reciprocating internal combustion engine can be lowered in partial load operation. On the other hand, the time-based lift characteristics which can be transferred by valve trains of intake and/or exhaust valves of a reciprocating internal combustion engine can be altered by a lift switchover and therefore adapted to the current operating state of the reciprocating internal combustion engine depending on operating parameters such as the engine speed and the engine load, whereby the engine power and the torque can be increased and the specific fuel consumption of the reciprocating piston engine can be reduced.
In the case of deactivatable valve trains, two mutually relatively displaceable or rotatable components of a switchable lift transfer element are usually provided in each case, of which the one component is in adjusting communication with the associated cam of a camshaft and the other component is in adjusting communication with the valve shaft of the associated gas exchange valve. Both components can be mutually coupled or uncoupled via a coupling element, in most cases designed as a coupling pin. The valve lift of the associated cam is transferred to the relevant gas exchange valve in the coupled state, but not in the uncoupled state, which means that the gas exchange valve then remains closed. The coupling pin is usually axially movably guided in a bore of the one component and displaceable into a coupling bore of the other component. The coupling pin is held in a rest position by means of a spring element and, under the application of an adjusting force, is displaced in opposition to the restoring force of the spring element into an actuating position and retained there. In the case of deactivatable valve trains, the rest position of the coupling pin usually corresponds to the coupled state of the components of the lift transfer element and the actuating position corresponds to the uncoupled state of the components. The deactivatable lift transfer elements can be deactivatable bucket tappets, roller tappets, rocker arms, cam followers or supporting elements.
In the case of switchable valve trains, at least two mutually relatively displaceable or rotatable components of a switchable lift transfer element are provided in each case, of which the one component is coupled to an associated primary cam or a camshaft with a particular valve lift and to the valve shaft of the associated gas exchange valve, and the other component is in adjusting communication with an associated secondary cam of the camshaft with a greater valve lift or with a secondary lift. Both components can be mutually coupled or uncoupled via a coupling element, in most cases designed as a coupling pin. In the uncoupled state, the valve lift of the primary cam is transferred to the relevant gas exchange valve; in the coupled state, on the other hand, the valve lift of the secondary cam is transferred to the gas exchange valve. The coupling pin is also usually axially movably guided in a bore of the one component here and displaceable into a coupling bore of the other component. The coupling pin is held in a rest position by means of a spring element and, under the application of an adjusting force, is displaced in opposition to the restoring force of the spring element into an actuating position and retained there. In the case of switchable valve trains, the rest position of the coupling pin corresponds in most cases to the uncoupled state of the components of the lift transfer element and the actuating position corresponds to the coupled state of the components. Such switchable lift transfer elements are, for example, switchable bucket tappets, switchable rocker arms or switchable cam followers.
The adjustment of coupling elements of switchable lift transfer elements usually takes place hydraulically in that, via a solenoid switching valve, for example, a switching pressure line leading to pressure chambers of the coupling elements is alternately connected to an oil pressure source or depressurized. A known design of a switchable cam follower, which is equipped with a hydraulically adjustable coupling pin and is provided in a reciprocating internal combustion engine for lift deactivation of a gas exchange valve, is disclosed in DE 10 2006 057 894 A1. On the other hand, DE 10 2006 023 772 A1 describes a switchable cam follower with a hydraulically adjustable coupling pin, which is provided in a reciprocating internal combustion engine for lift switchover of a gas exchange valve.
If gas exchange valves of a reciprocating internal combustion engine are to be selectively deactivated or switched over in groups, separate switching pressure lines, each with an associated switching valve, are required for a hydraulic adjustment of the coupling elements. A corresponding hydraulic adjusting device for selectively adjusting the coupling elements of a variable valve train in groups in a reciprocating internal combustion engine having two intake valves and two exhaust valves for each cylinder is described, for example, in DE 102 12 327 A1.
The switchable lift transfer elements of this valve train are formed as switchable bucket tappets in this case.
However, the adjustment of coupling elements of switchable lift transfer elements can also take place electromagnetically in that the coupling elements are each in operative communication with an electromagnet, and the electromagnets are alternately energized or de-energized. A known design of a switchable cam follower, which is equipped with an electromagnetically adjustable coupling pin and is provided in a reciprocating internal combustion engine for lift deactivation of a gas exchange valve, is revealed in U.S. Pat. No. 5,544,626 A. The coupling pin and the electromagnet, the armature of which is connected to the coupling pin, are arranged lengthwise in the primary housing of the cam follower, resulting in a greater structural length of the cam followers and a correspondingly greater width of the relevant cylinder head.
On the other hand, in the non-prepublished DE 10 2016 220 859 A1, a valve train of a reciprocating internal combustion engine with electromagnetically switchable cam followers is described, which is provided in a reciprocating internal combustion engine for lift switchover of the relevant gas exchange valves. The coupling pins are each arranged lengthwise in the respective primary lever of the cam followers and can each be brought into contact with a ramp surface of an armature rod of an associated electromagnet and displaced axially into a coupling position. The electromagnets are arranged with a substantially vertical alignment above the cam followers and the associated camshaft on a carrier plate fastened to the relevant cylinder head, resulting in a greater structural height of the cylinder head.
Further switchable cam followers with coupling pins aligned parallel and transversely to the longitudinal extent thereof are known from DE 101 55 801 A1 and DE 10 2015 221 037 A1. Moreover, U.S. Pat. No. 6,499,451 B1 discloses a variable valve train of an internal combustion engine, in which the switchable cam followers associated with each valve are actuatable by means of a separate actuator in each case. In this case, these actuators each act on an arm of a two-armed pivot element, which is pivotably mounted on a shaft and whereof the second arm can act on a coupling pin of the associated cam follower. This valve train is also regarded unfavorably, mainly on account of its many separate actuators and adjusting means.
Finally, J P 2004-108 525 A1 discloses a variable valve train with a plurality of cam followers for actuating functionally identical valves of an internal combustion engine, whereof the respective adjusting device manages with only one actuator. However, the secondary levers and primary levers therein are formed separately and arranged adjacent to one another. The secondary levers can be coupled to a directly adjacent primary lever via an axial displacement of a coupling pin mounted in a transverse bore of the respective secondary lever into a coupling bore of the respective primary lever. In the coupled state, the respectively greater lift of the primary and secondary cams of a camshaft is transferred to the relevant gas exchange valves. The axial displacement of the coupling pins can only take place in each case when both cams are followed on the base circle at the same time since only then are the transverse and coupling bores flush with one another.
The actuation of the coupling pins takes place by means of an adjusting device, which has a switching rod which is arranged parallel to the camshaft of the internal combustion engine and is linearly displaceable by an actuator. For each primary lever and secondary lever pair, two axial stops are fastened to the switching rod. A guide sleeve is arranged on the switching rod between two stops in each case, which guide sleeve is displaceable between the two stops on the switching rod, spring loaded in the switching direction on one side by means of a pressure spring. An arm, which is in actuating contact with the free end face of the said coupling pin, extends in one piece from the respective guide sleeve. In this case, the respective arms of the respective guide sleeves are formed as rigid metal levers. The coupling pin can be restored into its uncoupling position by means of a pressure spring.
When the switching rod is displaced in the switching direction, the secondary levers of the currently switchable lever pairs are immediately coupled to the primary levers. The coupling pins of the currently non-switchable lever pairs are pre-tensioned with a force in the switching direction by the tension of the relevant pressure springs. The coupling of the secondary levers to the primary levers takes place in each case when the relevant two cams of the associated camshaft are followed on the base circle and the transverse and coupling bores are flush with one another.
Since the arrangement of separate hydraulic switching pressure lines or electrical switching lines in a cylinder head of a reciprocating internal combustion engine is relatively difficult and costly owing to confined space conditions, and the variable valve train known from JP 2004-108 525 A1 was regarded as too mechanically complex, the object on which the disclosure was based was to propose a variable valve train of a reciprocating internal combustion engine of the type mentioned at the outset with switchable cam followers for functionally identical gas exchange valves, which can be switched over by means of a space-saving adjusting device. To this end, only one adjusting device for the switching cam followers shall be used in each case for actuating functionally identical valves.